ESSE 2220 – Lab 2 Report¶

Part 1¶

Course: ESSE 2220
Lab Title: Software Debouncing with GPIO Date Performed: 2025-09-19
Date Submitted: 2025-09-26

1. Names & Group Info¶

Group Number: GROUP 5
Members: Yathharthha Kaushal · Owen Oliver

2. Circuit Setup¶

GPIO Pin Used for LED: GPIO 17 GPIO Pin Used for Push Button: GPIO 18

We connected the LED (with resistor) to GPIO 17 and ground, and we connected the pushbutton to GPIO 18.

Schematic / Wiring:
image.png

3. Output:¶

image-2.png

4. Observations:¶

bouncetime (ms) What happens when I press once? What happens when I press quickly?
0 It flickers on and off randomly Same thing but more flickering
50 Works normally Sometimes it flickers randomly, but works most of the time.
100 Works perfectly Occasional double presses
200 Works as expected Doesn't recognize consecutive presses within 200ms of the first press
300 Works as expected Doesn't recognize consecutive presses within 300ms of the first press
500 Works as expected Doesn't recognize consecutive presses within 500ms of the first press
1000 Works as expected Doesn't recognize consecutive presses within 1000ms of the first press

5. Analysis¶

Which debounce value worked best for your button? Why?¶

Based on our observations, 100ms worked best for our button setup. This value provided the optimal balance between:

  • Reliability: It eliminated the random flickering that occurred with lower debounce times (0ms and 50ms)
  • Responsiveness: Unlike higher values (200ms, 300ms, 500ms, 1000ms), it still allowed for reasonably quick consecutive button presses
  • Practical usability: While 200ms+ values worked perfectly for single presses, they became too inefficient for faster presses.

At 100ms, we observed "occasional double presses - which isn't something we can eliminate (without re-introducing random flicker if we decrease the bouncetime)" during rapid pressing, which indicates we're right at the threshold where the debouncing is effective but not overly conservative.

In your own words, what is "button bounce" and why do we need debouncing?¶

Button bounce occurs when we press/depress a mechanical button/switch. Instead of making a clean, instantaneous electrical connection, the metal contacts inside the button physically "bounce" against each other multiple times in rapid succession (typically within a few milliseconds).

It's essentially like dropping a ball - it doesn't just hit the ground once and stop - it bounces several times before settling.

Why we need debouncing:

Without debouncing, our microcontroller reads these rapid on/off signals as multiple separate button presses instead of just one. This causes unwanted behavior like:

  • LEDs flickering randomly when it's pressed once
  • Button press triggering a mechanism too many times in quick succession
  • Unreliable input detection from the buttons

Software debouncing solves this by ignoring any additional button state changes for a specified time period after the first detected change, ensuring that one physical button press registers as exactly one logical button press in our code.